There are several limitations which should be considered when interpreting the results of this study, or if this study was to be replicated in future. Firstly, only 25 participants out of the 44 CI users from the SCIP who fulfilled the participant inclusion criteria were able to participate in the study. Many of the participants lived out of the city, and scheduling a time for them to attend a testing session at the University Clinic was often unfeasible. Some of the participants could not be contacted to arrange for a testing session, whilst others were not coming into the city during the time period of this study. A longer time frame or a follow-up study could have helped recruit a greater number of participants.
Secondly, pre-surgery testing was performed using 5 dB steps where as post-surgery testing was done using 2 dB steps. Using 2 dB steps in at least one pre-surgery test is recommended for future clinical assessment in order to provide greater accuracy when comparing to post-surgery thresholds. This will be particularly relevant when the surgeons want to assess the effectiveness of any modified surgical techniques or procedures. To allow for control over factors such as the progressive loss of hearing levels post-surgery, a longitudinal research design could be adopted where pre- and
post-surgery hearing tests are conducted at specific time intervals post-implantation for al the participants (e.g. 1 month, 3 months, 6 months, 12 months etc.).
Thirdly, none of the 13 participants that presented with residual hearing were currently using a HA in conjunction with the CI. A future study to evaluate the potential benefit that the HA may provide could be done using these participants with the results compared to this study.
The clinical implications of the results from the current research include that current, as well as future implantees through the SCIP who present with residual hearing should be encouraged to use a HA in their contralateral ear, along with their CI. This would allow them to maximise the benefits of both electric as well as low-frequency acoustic hearing. Additionally, the results from this study could be used to evaluate the efficacy of the new modified surgical techniques or strategies that the surgeons in the SCIP are beginning to implement. Should there be a further improvement in post-surgery outcomes, this could translate into expanding the candidacy criteria for a CI to include those persons with better hearing thresholds.
Finally, this study has demonstrated that like many overseas programs, cochlear implantation in New Zealand provides significant speech perception benefit for those with a significant sensorineural hearing loss. The mean open-set sentence perception improvement from 19% pre-surgery to 82% post-surgery is a clinically significant change. This along with the suggestion of potentially even better post-surgery outcomes in the future could be used to lobby the government for increased funding to the CI
program. This would not only be to address the current waiting list, but to enable more people who could potentially benefit from a CI to be afforded the opportunity to obtain one.
8
Summary and conclusion
This study found that even in the absence of specific hearing preservation techniques being used during implantation surgery for participants of this study, some of the participants still presented with measurable levels of post-surgery residual hearing. Thirteen of the 25 participants (52%) presented with measurable levels of acoustic hearing in their implanted ear. Further, 13 participants had aidable hearing in their contralateral ear. The speech perception results obtained from this study suggest that these implant recipients are obtaining significant improvement in speech perception outcomes post-surgery. The current SCIP candidacy criteria for cochlear implantation includes having pre-surgery speech perception scores less than 40% correct in the best- aided condition, and less than 60% correct in the ear to be implanted. The significant pre- to post-surgery improvement in speech perception outcomes for the participants of our study is a clear reflection that the current speech criteria for used by the SCIP to evaluate cochlear implant candidacy is not too lenient.
This thesis has also suggested that current, as well as future implantees through the SCIP who present with residual hearing in their contralateral ear should be encouraged to use a HA along with their CI. This would allow them to maximise the benefits of both electric as well as low-frequency acoustic hearing. Furthermore, should there be a future improvement in post-surgery outcomes resulting from the new modified surgical techniques or strategies that the surgeons in the SCIP are beginning to implement, this could translate into expanding theSCIP’scandidacy criteria for a CI. However, this
would probably require additional funding in order to ensure that there are sufficient resources for increased patient numbers. The speech perception benefits demonstrated in this and many similar studies, along with the quality of life reported by a host of studies (Cohen, Labadie, Dietrich, & Haynes, 2004; Damen, Beynon, Krabbe, Mulder, & Mylanus, 2007; Mo, Lindbaek, Harris, & Rasmussen, 2004) should be communicated to the government and other funding bodies. With the continual improvements in CI outcomes, more hearing impaired people are, and will continue to benefit from a CI.
9
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(A) Pre-surgery thresholds
Implanted ear P articipant 250 H z 500 H z 750H z 1000 H z 1500H z 2000 H z 3000 H z 4000 H z 6000 H z 8000 H z 1 60 80 90 95 90 85 80 95 N R N R 2 60 70 80 105 120 N R 115 N R N R 3 65 75 85 100 105 110 120 N R N R N R 4 55 75 95 100 115 N R N R N R N R N R 5 60 70 85 105 110 105 120 115 N R N R 6 30 35 95 100 105 105 N R N R N R 95 7 55 55 65 65 70 95 110 N R 8 20 90 105V T 120 115V T N R 9 65 70 90 110 N R N R N R N R 10 65 75 90 95 95 90 95 100 N R N R 11 90 100 95 110 95 100 90 12 70 80 85 90 110 N R N R N R N R N R 13 65 70 85 90 95 N R N R N R N R N R 14 50 105 115 115 115 115 110 105 15 100 100 110 110 115 N R N R N R N R 16 100 105 115 110 115 N R N R N R N R N R 17 N R 95 N R N R N R N R N R N R N R N R 18 35 65 85 105 120 120 115 N R N R N R 19 70 85 95 100 N R N R N R N R N R N R 20 95 95 95 95 90 90 90 90 95 95 21 75 95 105 105 110 115 115 N R N R N R 22 80 80 90 75 75 65 23 45 95 110 115 120 120 120 N R N R N R 24 75 100 115 115 N R N R N R N R N R 25 15 80 105 110 115 115 115 N R N RUnimplanted ear Participant 250 Hz 500 Hz 750Hz 1000 Hz 1500Hz 2000 Hz 3000 Hz 4000 Hz 6000 Hz 8000 Hz 1 60 100 NR 100 110 115 120 NR NR NR 2 85 90 95 120 NR NR NR NR NR 3 65 80 100 105 110 110 115 NR NR NR 4 85 85 90 95 100 105 110 110 NR NR 5 50 60 80 110 110 115 105 NR NR 6 40 55 70 95 110 110 115 NR NR NR 7 60 60 75 80 75 80 85 100 105 8 15 45 90 110 120 NR NR NR 9 50 55 90 110 90 100 NR NR 10 NR NR NR NR NR NR NR NR NR NR 11 NR NR NR NR NR NR NR NR NR NR 12 65 75 75 80 90 105 NR 110 NR NR 13 65 70 95 90 90 NR NR NR NR NR 14 20 70 110 110 110 115 NR NR 15 85 90 95 105 115 NR NR NR NR 16 NR 105 110 110 110 NR NR NR NR NR 17 NR NR NR NR NR NR NR NR NR NR 18 45 55 65 80 115 110 110 NR NR NR 19 110 NR 115 110 120 110 105 120 NR NR 20 110 105 105 110 NR NR NR NR NR NR 21 100 110 110 110 110 115 NR NR NR NR 22 20 35 75 95 90 90 70 60 23 45 100 110 115 110 120 120 NR NR NR 24 65 90 110 105 100 100 95 95 80 25 10 45 105 105 115 115 110 NR NR
